I've just strapped a ceiling with 1 x 2's and want to add a light fixture and wire it to an existing wall switch. Can I use BX cable as a protected cable and a saucer box before we install the new drywall ? Only the BX would be entering the box. I would use an angle box connector at the back KO. Would that be code compliant ? There is no attic space to access and I don't want to break the existing old ceiling drywall.
Im assuming you mean mc cable. Bx hasn't been used in a very long time. It sounds like you would be fine with either mc or romex. As long as its behind sheetrock either is fine. Make sure to add nail plates where you can so nobody sinks screws or nails into your wires